1. Field of the Invention
The present invention relates to the field of chemistry and its object is a general method for obtaining polyols, in particular polyesterols, from polyethylene terephthalate (PET), in particular PET production residuals or consumption waste, and variants to this method and products obtained, especially destined to the production of cellular materials such as polyurethane foams (PUR), and polyisocyanurate foams (PIR).
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
It is called to mind that the manner of preparing polyols by degradation of the polyethylene terephthalates by an inverse reaction of their synthesis reaction, so-called xe2x80x9cglycolysisxe2x80x9d, according to which the PET is heated in the presence of an excess of glycol (GLY), for example the monoethylene glycol (MEG), has been known for a long time. The major inconveniences of the polyols thus obtained in regard to their destination are their propensity for precipitating solids during their storage at ordinary temperature, as well as their elevated viscosity.
A recent prior art reference has proposed various solutions to attempt to remedy these inconveniences. For example, DE 3,435,014 (BAUER), EP 0,248,578 (BENTLEY et al.), U.S. Pat. No. 4,539,341 (HALLMARK), U.S. Pat. No. 4,559,370 (BLANPIED), U.S. Pat. No. 4,652,591, and U.S. Pat. No. 4,714,717 (LONDRIGAN) have proposed an esterification of the obtained polyols, whereas the patents EP 0,134,661 (CHARDONOL), U.S. Pat. No. 4,485,196 (SPERANZA), U.S. Pat. No. 4,604,410, and U.S. Pat. No. 4,701,477 (ALTENBERG) have proposed to modify them by ethoxy propoxylation. Other patents such as U.S. Pat. No. 4,468,824 (GRIGSBY), U.S. Pat. No. 4,485,196 (SPERANZA), U.S. Pat. No. 4,536,522 (GRIGSBY), U.S. Pat. No. 4,459,370 (BLANPIED), U.S. Pat. No. 4,642,319 (MCDANIEL), U.S. Pat. No. 4,644,019 (MCDANIEL), U.S. Pat. No. 4,714,717 (LONDRIGAN), U.S. Pat. No. 4,760,100 (MCDANIEL), Chem. Abs. 151, 159 (PENCZEK) have proposed to operate the distillation of the MEG simultaneously and proportionately of its formation resulting from the glycolysis.
However, the polyols obtained by the aforecited methods are mixtures of polyols having a high heterogeneity or dispersion in their molecular weights and lead therefore, during their cross linking or linking to PUR or PIR, to irregular, three-dimensional cross-linked systems, which is generally considered to be an unfavorable characteristic resulting from the presence of higher oligomers having a weak hydroxyl value ( less than 200 mg KOH/g) and of free glycols having an elevated hydroxyl value ( greater than 800 mg KOH/g). There has in addition been observed (G. TERSAC et al. in CELLULAR POLYMERS, Vol. 14, p. 14, 1995) another unfortunate consequence of this heterogeneity, i.e. a substantial increase of the viscosity.
One solution to limit the formation of higher oligomers would consist in effecting the glycolysis/esterification at elevated molar ratio of the glycol rests with respect to the diacid rests, then to eliminate the free glycols, by distillation. One would find oneself however in this case in an unbalanced chemical system, and the alcoholysis reactions would tend to reform free glycols as well as more condensed species.
A patent U.S. Pat. No. 4,758,607 (HALLMARK) describes a method permitting to eliminate the free glycols, without that they reform themselves of the MEG by rebalancing reaction; the polyols thus obtained have a very low proportion of free MEG, they are less viscous, present a better stability during storage and lead to foams having a larger density. However, the method has the inconvenience to require a high-vacuum distillation, continuously and with film scraping, which requires a very expensive installation. This patent cites numerous examples of glycols and polyols having a low molecular weight that can be utilized as glycolyzing agents, as well as numerous polyacids that can be taken as prior art to the present application. It should however be noted that the glycolysis catalyst cited (tetrabutyl orthotitanate) is not suitable for carrying out the invention.
It is recalled that the glycolysis reaction is a balanced reaction of the transesterification type. Catalysts of this reaction are well known in the art. Reference is made for example to the U.S. printed patent document 2,465,319 (WINFIELD) which cites salts such as the manganese acetates and zinc acetates or also amines such as the triethyl amines and tributyl amines. This catalysis of the glycolysis, and of the concomitant transesterification, is well mentioned in the patent U.S. Pat. No. 3,907,868 (CURRIE).
This latter patent disclosed also the manner to avoid the rebalancing of the reaction by deactivating (sequestering) the catalyst by means of agents such as phosphoric acid, phosphorous acid, aryl esters, alkyl esters, cykloalkyl esters, arylalkyl esters of these acids, the aliphatic and aromatic carboxylic acids such as the oxalic acids, citric acids, tartaric acids, terephthalic acids, tetrasodic salts of the ethylene-diamine-tetracetic acid, the phenyl phosphinic acid, as well as analogous products. It is however important to note that the technique disclosed by this publication is not the technique of the present invention and does not suggest it; it does not have the same objectives enumerated hereafter since it is directed to obtain from PET not polyols but dimethylterephthalate. The deactivating agents cited in this publication are however taken as prior art in the present application.
In a general manner, the glycols as glycolysis reagents, as well as the glycolysis catalysts or transesterification catalysts and the deactivating agents cited in the above recited publications are considered as possible reagents suitable for the carrying out of the present invention.
The general goal of the present invention is to propose a method for obtaining polyols, more particularly polyesterols, having a narrow molar dispersion, from PET waste, in simple reactors and provided with means of subjection to a low vacuum of, for example, between 1 and 50 mmHg.
The more particular objects of the invention are:
the obtaining of liquid polyols which are stable during storage, having a sufficiently low viscosity to permit an easy manipulation, and suitable for the preparation of cellular materials PUR or PIR having a strong and durable thermal insulation capacity;
the obtaining of polyols having a good solubilizing capacity of chlorofluorohydrocarbons (HCFC) foaming agents (expanding agents), particularly the HCFC 141b, i.e. at least 20 %-weight of HCFC 141b, without for this reason the gaseous HCFC 141b contained in the cells being able to dissolve later in the matrix PUR or PIR, thus, polyols leading to a matrix PUR or PIR having a low affinity for the HCFC;
the obtaining of polyols having a narrow molar distribution, i.e. polyesterdiols essentially comprised of oligomers, polyesters, xe2x80x9cmonomersxe2x80x9d, and xe2x80x9cdimersxe2x80x9d and containing very little higher oligomers and free glycols;
the obtaining of polyols having a reduced content in difunctional free glycols, compatible with multifunctional glycols capable of leading to rigid PUR systems netted after an addition of limited quantities of multifunctional polyols;
the obtaining of polyols having a functionality higher than two, at a narrow molar distribution;
the obtaining of polyols in simple reactors, i.e. having the capacities providing only for means for stirring, for the introduction of an inert atmosphere (N2), for heating up to 220-240xc2x0 C., for total reflux or distillation, for filling or drawing off, and being able to function under atmospheric pressure and under vacuum (pressure of 3 mmHg and more);
the obtaining of polyols with a method performing a distillation of free glycols and permitting an internal recycling of the distillate;
finally, the obtaining of polyols by a method based on the glycolysis/esterification of PET with: short reaction times and a distillation of free glycols which do not entrain rebalancing and reequilibrating reactions.
According to the invention, a method for obtaining polyols comprises in a first step to react glycols, i.e. polyalcohols having a functionality at least equal to two (MEG, DEG, DPG, . . . ), on polyethylene terephthalate (PET) in the presence of a transesterification catalyst (CAT), then, in a last step, to distill the free glycols (or freed glycols) and is characterized in its generality in that a step subsequent to the first step and before or simultaneously with said last step comprises the deactivation of the glycolysis catalyst by a deactivating agent (DES).
According to a first variant (I) of the general method, a second step, called esterification, following to the first glycolysis step comprises to introduce a polyacid (PLA) or its derivatives (anhydrides, . . . ) such as for example adipic acid, phthalic anhydride, etc. into the glycolysis medium.
Preferably, a strong acid such as the phosphoric acid H3PO4, which can at the same time constitute a deactivating agent (DES) of the catalyst of the preceding step (glycolysis), is chosen for catalyzing the esterification reaction of the second step of this first variant of the method.
The esterification step, carried out under atmospheric pressure but under inert atmosphere, can be accompanied by water formation which distills off.
The following step consists in the distillation under low vacuum (3 to 40 mmHg) of the free glycols formed during the preceding steps, which distillation leaves the desired polyols in the reaction chamber; according to the hydroxyl value (IOH) desired for these latter, one pushes the distillation all the longer because one looks for a weak IOH (200xe2x89xa6IOHxe2x89xa6400, 1 h less than t less than 3 h).
According to a second variant (II) of the general method, the second step, of esterification, consists in introducing into the glycolyzed medium one/several polyesters (PLE), such as dimethylesters (AGS), or also such as the mixture xe2x80x9cRHODIASOLV (registered markxe2x80x9d of RHONE-POULENC (dimethyl adipate, dimethyl glutarate, dimethyl succinate).
The following step of distillation, under low vacuum (3 to 40 mmHg) is preceded by the introduction of the deactivating agent (DES) into the reactive medium. The deactivating agent is, still preferably, phosphoric acid. It could also be an organic derivative of phosphorus, but with a weaker activity and lower efficacy.
One will note that, still according to the invention, the distilled glycols can be recycled during a following cycle.
According to a third variant (III) permitting to achieve the recited object of obtaining polyols having a functionality higher than two, one employs polyalcohols of a functionality higher than two, for example, triols such as the glycerol (GLR) in addition to DEG and to DPG for carrying out the glycolysis; this variant, in which a maximum quantity, in relation to the other variants, of introduced PET is transformed to polyols or, in other words, in which the ratio R, or yield,   R  =            polyols      ⁢              xe2x80x83            ⁢      produced              PET      ⁢              xe2x80x83            ⁢      introduced      
is maximum, is a particularly interesting variant from the economical point of view.
According to a fourth variant (IV), which is close to the preceding variant a mixture (AGS) of dimethyl esters is employed for operating a transesterification reaction. This variant which is a little less economical than the preceding variant permits to obtain a product of a lesser viscosity.